The most common optical connection used in manufacturing of optical devices is between an optical fibre end and a lens, such as a graded index (GRIN) lens. There are commonly two ways to make the connection. One common coupling system comprises a sleeve in which a fibre end within a supporting housing/ferrule is joined to a lens by attaching the sides of the ferrule and the lens to the interior bore of the sleeve. Manufacturing tolerances of, for instance, the lens diameter, the ferrule diameter, or the dimension and position of the bore within the ferrule, introduce variations which make it difficult to achieve accurate alignment using this type of connection. The sleeve must have a large enough internal dimension to accommodate a ferrule or lens at its largest tolerance. As a result, smaller elements may unintentionally become misaligned with respect to other components within the sleeve. The fibre end within the ferrule is not always concentric. When the ferrule internal diameter is too large for the fibre, the ferrule bore is not perfectly centred, or the fibre core is slightly off-centre, it becomes necessary to adjust, or tune, the alignment of the fibre to the lens. This is difficult within the confines of the prior art coupling sleeve. Temperature changes in the environment also cause different elements in the sleeve coupler to respond differently, further affecting the quality of the coupling. In many instances, it is preferred to have the fibre aligned at a port on the lens that is disposed adjacent to, rather than aligned with, the optical axis of the lens. This is not straightforward within a sleeve connection.
Another common practice is to couple an optical fibre to a lens, such as a graded index (GRIN) lens, by placing the optical fibre into a ferrule or fibre housing and joining an end face of the ferrule directly to a face of the lens by applying a layer of adhesive between them. A direct ferrule to lens adhesive connection facilitates alignment of the coupled elements and provides a uniform joint. Planar end faces of the lens and ferrule are reliably achieved to prevent unwanted tilt angle at the coupling. Positioning the fibre adjacent to the optical axis of the lens is possible without the confining sleeve coupler. Also, relatively easy alignment tuning is possible to compensate for eccentric fibre positioning within the ferrule. However, this method can only be used for lenses having flat surfaces which limits the applications of the method. Further, spacing between fibre and lens has to be accurately controlled which requires tight tolerance on the lens design.
To couple an optical fibre end to an optical element, such as a lens, several positioning variables exist: the spacing between the elements and the coupling point relative to the optical axis are two of them. Common coupling techniques do not provide a convenient method of adjusting the spacing between the elements and the coupling point at the same time.
It is often desired to make a coupling with a precise predetermined distance between elements, which is not practicable with a direct adhesive connection. Fixing the elements with the desired separation between them is typically accomplished by securing them on a substrate with adhesive. However, it is difficult to establish an exact separation and alignment by this method.
The use of a single sleeve into which the ends of the optical fibre and lens are placed only allows adjustment during tuning/alignment along a single axis, i.e., along the optical axis of the lens and the longitudinal axis of the ferrule. It would be advantageous to be able to provide additional directions for adjustment during tuning/alignment of an optical coupling.
It is desired to provide a coupling system, which provides a reliable means for coupling between optical elements. It is also desired to provide a coupling system, which can accurately control the spacing between optical elements, and provide adjustment to the alignment of the coupled optical elements.